Parse emoji from emoji-serenity.txt to allow displaying their names and
grouping them together in the EmojiInputDialog.
This also adds an "Unknown" value to the EmojiGroup enum. This will be
useful for emoji that aren't found in the UCD, or for when UCD downloads
are disabled.
This allows us to find emoji data for files such as /res/emoji/U+A9.png.
U+00A9 is not fully-qualified (its full form is U+00A9 U+FE0F). But the
UCD has unqualified data for this code point; generating it allows us to
categorize these emoji appropriately in the EmojiInputDialog.
According to TR #51, the "best definition of the full set [of emojis] is
in the emoji-test.txt file". This defines not only the emoji themselves,
but the order in which they should be displayed, and what "group" of
emojis they belong to.
